Synchronized SVPWM With Half-Wave Symmetry Relaxation for Low-Switching-Frequency Three-Level NPC Inverter

Half-wave symmetry (HWS) is generally considered as a necessary restriction when designing the switching sequences of synchronized SVPWM (SSVM), in order to eliminate even harmonic component and simplify analysis. However, the optimization space of switching sequences is reduced because of artificial restriction, which leads to suboptimal solutions. Furthermore, the pulse number can only be integer with the restriction of HWS, so the maximum allowable switching frequency of the inverter cannot be fully utilized. In this paper, SSVM with HWS relaxation for three-level NPC inverter is proposed. By optimizing switching sequences and allowing for noninteger pulse number, the proposed SSVM achieves lower harmonic distortion compared with conventional SSVM (CSSVM). The effectiveness of the proposed strategy is verified by simulations.